Abstract
The main objective of this paper is to improve the power sharing capability and to achieve synchronization between three-phase Uninterruptible power supply (UPS) units in the presence of load interruption. This paper presents a droop-controlled scheme in such a way that the computation of the instantaneous value of the active power and the reactive power are taken as feedback signals to the frequency and voltage restoration control system. The restored frequency and voltage are introduced to voltage controller circuit, which produces a suitable control signal to sinusoidal pulse width modulation circuit (SPWM). Thus producing a suitable trigger pulses to the inverter gate in order to guarantee synchronization between three-phase UPS units. Simulation of two UPS units with the same ratings (4 KW) are carried out using MATLAB. The results show the effectiveness of the proposed control system in achieving synchronization and improving the power sharing capability in the presence of load interruption. Keywords: Uninterruptible power supply; power sharing; parallel operation; droop control . DOI : 10.7176/JETP/9-4-02 Publication date : April 30 th 2019
Highlights
Uninterruptible power supplies are used to make electrical power system more reliable and continuous
Great efforts have been devoted to the study of power sharing control strategies for modular Uninterruptible power supply (UPS)
This paper presents a droop-controlled scheme based on measuring the instantaneous values of the active power and the reactive power on the tie line and taken these values as feedback signals to the frequency and voltage restoration control system
Summary
Uninterruptible power supplies are used to make electrical power system more reliable and continuous. Previous studies indicate that the control strategies require communication lines between the modules such as concentrated method, master slave method and distributed logic control method. This results in increasing the cost of the system, making it difficult to expand the system and the long distance communication lines will be easier to get interfered, thereby reducing system reliability and expandability, [3], [4], [5]. Research on control strategies without communication links has become very popular These strategies based on droop concept which improve reliability requirements in addition to avoiding the complexity and high costs. Low pass filters is introduced at the output terminals of each inverter to smooth out the waveform and makes it as close as possible to the required sine wave, [14]
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